This invention broadly relates to pollution control apparatus. More particularly, the present invention relates to a system for removing and recovering a contaminant solvent from a gas such as air or the like.
A variety of conventional industrial processes pollute air with organic solvent such as toluene or other organic hydrocarbons. Prior art systems have been developed which attempt to both purify the air and recover at least a portion of the contaminant solvent. At present most known solvent recovery processes depend mainly on the process of adsorption. For higher solvent concentrations absorption in oil can be used, but the solvent concentration should be generally above 1%. At lower solvent concentrations the adsorption capacity of a certain amount of activated charcoal is much larger than the absorption capacity of the same amount of oil.
In existing solvent recovery processes solvent may be stripped from either charcoal or oil by steam injected into the sorption medium. However, direct steam stripping can result in relatively large amounts of condensed steam which are unsuitable for recirculation. Solvents dissolved in water may therefore escape recovery, unless costly distillation processes are attempted. Furthermore, dissolved solvents create a serious water pollution problem. Since most solvents are chemically inert their removal or breakdown through conventional biological processes is exceedingly inefficient.
A problem with adsorption processes is the characteristic sensitivity to irreversible contamination. Contamination can be caused either by the presence of particulate material or specific gases in the airstream. Also, replacement of charcoal in an adsorption system is much more difficult than replacement of oil in an absorption system. When a gas to be treated contains silicone oil, for example, in addition to hydrocarbon solvents, adsorption purification systems will be deleteriously affected as the silicone oil adheres to the charcoal granules.